This invention relates to electrical cardiac therapy devices, specifically to emergency defibrillators, cardioverters and pacemakers.
Electrical therapy is commonly used in cardiac therapy, especially in cardiac resuscitation. Defibrillation, cardioversion and pacemaker therapy play a major role in cardiac resuscitation. Defibrillators and cardiac pacemakers are indeed common devices in the emergency armamentarium. Electrical therapy has proved over the last two decades to be often lifesaving in cardiac arrest settings. Cardiac arrest can result from a variety of cardiac arrhythmias all amenable to electrical therapy. These arrhythmias include ventricular fibrillation, ventricular tachycardia, ventricular asystole and high degree heart blocks.
A defibrillator is a device that administers a controlled electrical shock to patients to terminate a cardiac arrhythmia. The technique of administering the electrical shock is usually referred to as defibrillation if it used to terminate Ventricular Fibrillation or pulseless Ventricular tachycardia. The technique is referred to as Cardioversion if it is administered for other cardiac arrhythmias, typically atrial fibrillation, atrial flutter, or ventricular tachycardia. Typically, in defibrillation the electrical shock is unsynchronized with the cardiac cycle while in cardioversion the electrical shock is delivered in synchronization with the cardiac cycle, at a specific electrical stage of the cardiac cycle.
The defibrillator basically consists of a charging circuit that gradually builds electrical energy to a preset level on a storage circuit. The storage electrical energy is then delivered to the patient through a discharge circuit. The electrical stored energy is delivered via conductive paddles applied to the chest or back of a patient in the External Defibrillator. Another type of Defibrillator is the Automatic Implantable Cardioverter-Defibrillator which consists of a pulse generator with both sensing and shocking electrodes. In the Automatic Implantable Defibrillator the shocking electrodes are usually two epicardial patches placed in anteroposterior position over the heart surface or one epicardial patch and another electrode, the so called transvenous spring electrode, placed in the right ventricular apex, all implanted by thoracotomy or sternotomy i.e. by surgical opening of the chest. Rarely is direct epicardial defibrillation implemented i.e. defibrillation with two epicardial paddles applied directly over the heart in anteroposterior position. Instances of application are traumatic cardiac arrest, open chest surgery or medical cardiac arrest during open chest cardiac massage.
The energy required for Direct or Internal Defibrillation of the heart in these cases is by far less than the energy required with External Defibrillation. Due to the fact that the paddles are directly applied over the heart, the impedance, i.e. the resistance to current flow, is greatly reduced in respect to the commonly used External Defibrillators. There are indications that Direct or Internal Defibrillation is more effective than External Defibrillation. Unfortunately due to the fact that Direct or Internal Defibrillation can be carried out only in patients victim of cardiac arrest via thoracotomy, its applications are severely limited and, practically, it can be carried out only in cases of traumatic cardiac arrest or in patients whose heart arrested during cardiac surgery in the operating room.
Pacemakers are medical devices that deliver an electrical stimulus through electrodes to the heart causing electrical depolarization and subsequent cardiac contraction. Emergency cardiac pacing is required in patients whose primary problem is cardiac impulse formation and br conduction such as hemodynamically compromising unstable bradycardia, high degree of heart block, bradysistolic cardiac arrest and also refractory tachycardias.
Emergency Temporary Cardiac Pacemakers are named according to the location of the electrodes and the pathway the electrical stimulus travels to the heart. They are named Transcutaneous when the electrodes are placed on the skin of the anterior chest wall and the back of a patient, Transvenous when the electrode tip is positioned in the right ventricle or right atrium or both, Transthoracic when the electrodes are placed through the anterior chest wall into the myocardium, i.e. the heart muscle, Epicardial when the electrodes are placed on the surface of the heart, and Transesophageal when the electrodes are positioned within the esophagus.
As in Internal Defibrillation, Epicardial pacing is almost exclusively carried out during open chest surgery for resuscitation of patients with penetrating chest trauma. There are studies documenting the dramatically superior efficacy of epicardial pacing versus the transcutaneous pacing. However, despite dramatic improvement following epicardial pacing, its application is restricted to only a handful of patients due to the obligate requirement of opening surgically the chest for placing the pacing electrodes onto the heart surface.
No epicardial electrical therapy device, Defibrillator or Cardiac pacer, is known to have the electrodes placed onto the heart surface without the surgical opening of the chest with sharp instruments. Such a procedure, besides being associated with high morbidity and mortality, has the unavoidable drawback of having to be carried out only in operating rooms and rarely in Emergency Departments. Due to the invasiveness character of the procedure, epicardial defibrillation and or pacing is presently carried out only in cases when open chest cardiac massage via thoracotomy is carried out.